This invention relates to a plant for processing surplus concrete comprising a receiving bin having mutually opposite end walls, two side walls, a bottom and a top covering grate, also comprising a washing apparatus for separating the surplus concrete into a plurality of components, such as sand and gravel, on the one hand, and very fine components, on the other hand, which latter are entrained by rinsing water discharged at one end of the washing apparatus whereas the first component is discharged at the opposite end of the washing apparatus, also comprising an inclined transfer duct, which adjoins the inclined bottom of the receiving bin and connects the receiving bin to the washing apparatus, and discharge control apparatus for controlling the discharge of surplus concrete from the receiving bin in dependence on the free processing capacity of the washing apparatus.
Such plant is known from German Pat. No. 30 34 451. The discharge control apparatus consists of a flap, which is suspended like a pendulum and by means of a positioning motor is to be actuated in dependence on the driving power of the washing apparatus in such a manner that the flap is closed in response to an increase of the driving power of the washing apparatus and is reopened in response to a subsequent decrease of the driving power. The receiving bin has a cubic capacity of about 1 cubic meter. A vehicle from which 5 cubic meters of surplus concrete are to be discharged can be discharged only in a plurality of batches corresponding to the capacity of the washing apparatus, which may be able to process, e.g., 5 cubic meters per hour. In that case the vehicle will have to wait for one hour. The control of the discharge flap in dependence on the power requirement of the washing apparatus as taught by German Pat. No. 30 34 451 is not optimum. If the receiving bin is full and the flap is opened, a large quantity of surplus concrete will be instantaneously delivered to the washing apparatus. But the power input of the rotary drive of the washing drum will not considerably increase until the fine and coarse components are lifted by the scooping buckets and only thereafter can the flap be closed. The quantity of surplus concrete which has entered the washing drum before that time is larger than would be permissible for an optimum cut of about 0.2 mm.